Turpentine is the general term for the volatile oil present in trees, primarily coniferous trees. Chemically, it is predominately a mixture of unsaturated mono- and bi-cyclic C.sub.10 H.sub.16 hydrocarbons. The principal component is alpha-pinene, which is present in the turpentine from all species of turpentine bearing trees.
The composition of the turpentine is determined by the species of the tree. A chromatograph of the turpentine makes a good fingerprint for identifying the species.
Although over thirty compounds have been identified in turpentine only a few have commercial significance, that is, they can be separated in high purity for subsequent use. Alpha-pinene, beta-pinene, and beta-phellandrene and dipentene are present in large enough volume in gum or sulfate turpentines of most species to make isolation feasible. .DELTA.-3 carene is present in large quantities in certain species, especially in the northwestern and Scandinavian pines. The terpenes, as one would expect, will undergo numerous reactions including hydrogenation, isomerization, polymerization, oxidation, halogenation, esterification and dehydrogenation.
There has been and continues to this day investigations concerning the production of high volume chemicals from nonpetroleum base sources. Trees, especially, coniferous trees, are a renewable resource that can be ground into wood chips and have extracted therefrom resins and terpenes. Terpenes are therefore a renewable resource that may be used to replace the present petroleum based source of most of industry's hydrocarbons. However, a turpentine or a mixture of terpenes, in and of themselves, are not a commercially significant hydrocarbon feed stock. Therefore, a process that will readily convert a terpene or a turpentine feed stock into a valuable or commercially more acceptable compound is highly desirable.
In the past numerous publications have reported the conversion of turpentine to various chemical compounds using numerous reaction conditions and catalysts. More specifically, Mizrahi and Nigam, (J. Chromatog., 25 (1966) pp. 230-241) report the dehydrogenation of seven monoterpenes to para-cymene using catalytic dehydrogenation in a reaction gas chromatograph on a micro scale. Mizrahi and Nigam disclose the use of platinum on alumina to obtain p-cymene from hydrocarbons.
The prior art also discloses the vapor phase dehydrogenation of pinene to p-cymene through the use of platinized charcoal. (J. Chem. Soc. (1940) pp 1139 to 1147) Further, various terpenes including limonene have been dehydrogenated to p-cymene using sulphur. See A. R. Pinder, The Chemistry of Terpenes, Wiley, 1960, p 43. Also, substituted .alpha.-methylstyrene has been prepared by acid catalyzed dehydration of the corresponding alcohol. (Chemical Week, July 30, 1980, p 25)
However, none of the prior art publications disclose or suggest the process for the conversion of terpenes to DMS which comprises contacting at least one terpene selected from the group comprised of mono- and bi-cyclic unsaturated hydrocarbons having the formula C.sub.10 H.sub.16 ; with an alkali metal hydroxide catalyst on a support at a temperature of 300.degree. to 500.degree. C. at a liquid hour space velocity (LHSV) of 0.20 to 20.